In an attempt to quantify the affect on photometry due to contamination from bright star diffraction spikes and confusion, Rae Stiening has generated a set of simulated raw Ks survey data by placing 8 artifical stars around a Ks=8.0 mag primary in an existing 2MASS scan. Here is Rae's description:
8/9/2000 I am sending to holly:/k2/ftp/north at this time substitutes for scan k0369133.rdo in which 8 guest stars have been added. The 8 guest stars have been added equally spaced on a circle of radius 17 NICMOS pixels (about 34 arc seconds). The parent star is at the center of the circle of guest star clones. It is an 8th K magnitude star at 13h34m21.95s +30d29m20.7s. The files are named as follows: kfakmag09.rdo guest stars are 9th magnitude kfakmag13.rdo guest stars are 13th magnitude kfakmag14.rdo guest stars are 14th magnitude kfakmag15.rdo guest stars are 15th magnitude The guest stars are in six frames including frame 243. The compressed image on the IPAC image surver is called ki1330244.fits. Four of the guest stars are located so that they will be contaminated by the diffraction spikes of the parent. (though not much) So lets run these scans and see what happens. Rae 8/14/2000 The following Admirals' Club variants of k0369133.rdo are enroute to holly. I didn't fix the missing star problem so for the north star we may have to account for 5/6 images on some of these runs. KFKMAG16.RDO KFKMAG17.RDO The above to data sets continue the 17 pixel radius star cluster down to the detection threshold. Cluster magnitudes are indicated in the file names. KFLMAG09.RDO KFLMAG13.RDO KFLMAG14.RDO KFLMAG15.RDO KLFMAG16.RDO The above data have a 8 pixel radius star cluster with the magnitudes indicated in the file names. KFMMAG09.RDO KFMMAG13.RDO The above two files have a 5 pixel radius star cluster with the magnitudes indicated in the file names. Rae 8/16/2000 I'm sending two more Admiral's club runs to holly:/k2/ftp/north. These are a 5 pixel radius circle at 14th and 15th magnitude. This just extends the range of contaminated stars fainter. (we only did 13 so far) Rae The runs are kfmmag14.rdo and kfmmag15.rdo Two more fake data files are being sent to holly:/k2/ftp/north. KFD1.RDO 5 pixel radius circle 15 pixels displaced from parent 8th magnitude star. KFD2.RDo 5 pixel radius circle -15 pixels displaced from parent 8th magnitude star. Rae
The modified Ks *.rdo files were combined with the corresponding real J and H *.rdo files for this scan and run through the operational 2MAPPS system using the appropriate flat and dark data for that night.
The bright star in the above image has a calibrated magnitude of Ks=8.001+.039. Its reconstructed RA and DEC are 203.591498 +30.489037 (J2000).
The following images show Ks Atlas Images with the artifical stars of different brightnesses placed at 17 pixel (34") separation from the primary star.
All of the artificial stars were detected in the standard pipeline point source lists down to the 15th magnitude set. Half of the 16th magnitude apparitions were detected and none of the 17th magnitude stars were found. The table below shows the extracted positions and Ks magnitudes for each source in each image. Since there were no simulations added to the J or H data, there were of course no detections (except for the original primary star). The rows in the following table correspond to primary and 8 simulated sources; the artificial stars are desribed by their directional offset from the master source. The sets of columns (ra,dec,mag,msig) correspond to the positions, Ks mag and magnitude uncertainty in run. The suffix describes the run (0=original data, 09=9th mag simulated sources, 13=13th mag simulated sources, etc.).
Note that although the photometry listed for the primary star in the original scan is calibrated, the simulated scan data did not have calibrations applied. Therefore, a small photometric zero point offset of ~+0.034 mag should be added to the simulated star photometry to restore the original calibration.
| src | ra09 | dec09 | mag09|msig09| ra13 | dec13 | mag13|msig13| ra14 | dec14 | mag14|msig14| ra15 | dec15 | mag15|msig15| ra16 | dec16 | mag16|msig16| ra17 | dec17 | mag17|msig17| | char|double|double| double | double |double|double| double | double |double|double| double | double |double|double| double | double |double|double| double | double |double| double | double |double| master 203.591491 +30.489061 7.979 0.038 203.591491 +30.489059 7.961 0.039 203.591480 +30.489065 7.959 0.037 203.591478 +30.489069 7.967 0.038 203.591483 +30.489065 7.965 0.038 203.591477 +30.489073 7.982 0.038 N 203.591586 +30.498455 9.166 0.035 203.591586 +30.498484 13.150 0.050 203.591544 +30.498489 14.130 0.079 203.591564 +30.498461 15.106 0.167 0.000000 +0.000000 0.000 0.000 0.000000 +0.000000 0.000 0.000 NE 203.599224 +30.495661 8.992 0.036 203.599237 +30.495682 12.942 0.045 203.599208 +30.495695 13.881 0.067 203.599218 +30.495674 14.770 0.121 0.000000 +0.000000 0.000 0.000 0.000000 +0.000000 0.000 0.000 E 203.602395 +30.489035 8.981 0.036 203.602402 +30.489059 12.950 0.050 203.602366 +30.489080 13.875 0.073 203.602369 +30.489075 14.791 0.135 203.602378 +30.489069 15.597 0.263 0.000000 +0.000000 0.000 0.000 SE 203.599149 +30.482443 8.983 0.037 203.599136 +30.482466 12.957 0.046 203.599074 +30.482487 13.924 0.067 203.599016 +30.482464 14.868 0.129 203.598887 +30.482470 15.683 0.265 0.000000 +0.000000 0.000 0.000 S 203.591434 +30.479729 8.963 0.039 203.591450 +30.479752 12.946 0.049 203.591394 +30.479799 13.898 0.073 203.591369 +30.479843 14.858 0.141 0.000000 +0.000000 0.000 0.000 0.000000 +0.000000 0.000 0.000 SW 203.583758 +30.482515 8.941 0.038 203.583764 +30.482542 12.960 0.048 203.583728 +30.482553 13.870 0.066 203.583722 +30.482540 14.780 0.123 203.583847 +30.495829 15.536 0.240 0.000000 +0.000000 0.000 0.000 W 203.580599 +30.489136 8.964 0.036 203.580605 +30.489178 12.924 0.048 203.580582 +30.489208 13.864 0.072 203.580624 +30.489237 14.812 0.140 0.000000 +0.000000 0.000 0.000 0.000000 +0.000000 0.000 0.000 NW 203.583838 +30.495731 8.979 0.036 203.583854 +30.495770 12.944 0.046 203.583812 +30.495796 13.875 0.068 203.583831 +30.495808 14.766 0.125 203.583847 +30.495829 15.536 0.240 0.000000 +0.000000 0.000 0.000
The following images show Ks Atlas Images with the artifical stars of different brightnesses at 8 pixel (16") separation from the primary star.
The table below lists the extracted source positions and Ks photometry for the primary and artificial stars in each simulation, as above. All of the artificial stars were detected down to the 15th magnitude case, but only one of the 16th magnitude simulated stars was detected. There was no 17th magnitude run at this separation. As above, the simulated scans were not calibrated so there is a +0.03 mag offset from the actual photometric scale.
| src | ra09 | dec09 | mag09|msig09| ra13 | dec13 | mag13|msig13| ra14 | dec14 | mag14|msig14| ra15 | dec15 | mag15|msig15| ra16 | dec16 | mag16|msig16| | char| double | double |double|double| double | double |double|double| double | double |double|double| double | double |double|double| double | double |double|double| master 203.591491 +30.489061 7.975 0.039 203.591478 +30.489063 7.965 0.037 203.591481 +30.489069 7.977 0.037 203.591482 +30.489067 7.977 0.037 203.591481 +30.489065 7.964 0.037 N 203.591521 +30.493492 8.971 0.038 203.591499 +30.493536 12.883 0.058 203.591505 +30.493528 13.832 0.093 203.591519 +30.493496 14.679 0.167 0.000000 +0.000000 0.000 0.000 NE 203.594716 +30.491829 8.984 0.038 203.594681 +30.491867 12.957 0.051 203.594678 +30.491871 13.962 0.083 203.594672 +30.491859 14.933 0.178 0.000000 +0.000000 0.000 0.000 E 203.596623 +30.489059 8.972 0.036 203.596581 +30.489115 12.947 0.050 203.596571 +30.489119 13.969 0.083 203.596521 +30.489101 14.982 0.188 0.000000 +0.000000 0.000 0.000 SE 203.594696 +30.486320 8.969 0.034 203.594654 +30.486347 13.001 0.052 203.594629 +30.486334 14.060 0.085 203.594675 +30.486219 15.132 0.202 0.000000 +0.000000 0.000 0.000 S 203.591470 +30.484678 8.964 0.039 203.591409 +30.484726 12.899 0.053 203.591374 +30.484728 13.844 0.080 203.591304 +30.484726 14.671 0.138 0.000000 +0.000000 0.000 0.000 SW 203.588282 +30.486349 8.961 0.039 203.588259 +30.486393 12.913 0.049 203.588285 +30.486389 13.899 0.074 203.588351 +30.486376 14.826 0.151 203.588452 +30.486376 15.611 0.295 W 203.586363 +30.489111 8.948 0.038 203.586334 +30.489134 12.963 0.049 203.586347 +30.489092 14.017 0.078 203.586412 +30.488947 15.052 0.173 0.000000 +0.000000 0.000 0.000 NW 203.588311 +30.491856 8.986 0.037 203.588273 +30.491894 12.919 0.050 203.588270 +30.491888 13.918 0.078 203.588258 +30.491856 14.888 0.156 0.000000 +0.000000 0.000 0.000
The following images show Ks Atlas Images with the artifical stars of different brightnesses at 5 pixel (10") separation from the primary star.
The table below lists the extracted source positions and Ks photometry for the primary and artificial stars in each simulation, as above. All of the artificial stars were detected in both cases. As above, the simulated scans were not calibrated so there is a +0.03 mag offset from the actual photometric scale.
| src | ra09 | dec09 | mag09|msig09| ra13 | dec13 | mag13|msig13| ra14 | dec14 | mag14|msig14| ra15 | dec15 | mag15|msig15| | char| double | double |double|double| double | double |double|double| double | double |double|double| double | double |double|double| master 203.591491 +30.489059 7.958 0.043 203.591485 +30.489065 7.967 0.038 203.591481 +30.489071 7.974 0.037 203.591482 +30.489065 7.977 0.038 N 203.591516 +30.491837 8.960 0.060 203.591500 +30.491884 12.730 0.071 203.591512 +30.491922 13.585 0.093 203.591561 +30.491940 14.217 0.120 NE 203.593428 +30.490742 8.978 0.042 203.593402 +30.490746 12.719 0.078 203.593385 +30.490747 13.575 0.109 203.593428 +30.490738 14.214 0.151 E 203.594698 +30.489073 8.975 0.043 203.594644 +30.489130 12.821 0.068 203.594636 +30.489120 13.601 0.105 203.594431 +30.489075 14.115 0.147 SE 203.593413 +30.487431 8.938 0.043 203.593355 +30.487501 12.793 0.050 203.593351 +30.487507 13.725 0.080 203.593284 +30.487518 14.535 0.12 S 203.591489 +30.486332 8.938 0.049 203.591438 +30.486401 12.760 0.066 203.591421 +30.486437 13.585 0.087 203.591361 +30.486553 14.248 0.140 SW 203.589571 +30.487442 8.942 0.042 203.589542 +30.487507 12.852 0.103 203.589554 +30.487530 13.766 0.186 203.589526 +30.487602 14.658 0.280 W 203.588300 +30.489098 8.958 0.039 203.588268 +30.489161 12.961 0.035 203.588299 +30.489113 13.945 0.057 203.588294 +30.489256 14.896 0.152 NW 203.589585 +30.490738 8.940 0.050 203.589579 +30.490822 12.817 0.068 203.589607 +30.490774 13.681 0.084 203.589644 +30.490618 14.420 0.114
The table below lists the extracted positions and Ks magnitudes for the primary and 13th mag simulated sources in the rings displaced 15 pixels west (15w) and 15 pixels east (15e) of the primary star. The source names refer to the simulated star's location in their respective "rings", not their displacement from the primary star.
| src | ra15w | dec15w |mag15w|msig15| ra15e | dec15e |mag15e|msig15| | char| double | double |double|double| double | double |double|double| master 203.591482 +30.489067 7.977 0.037 203.591482 +30.489067 7.979 0.037 N 203.581840 +30.491940 12.928 0.062 203.601102 +30.491846 13.021 0.068 NE 203.583768 +30.490824 12.984 0.062 203.602992 +30.490747 12.923 0.058 E 203.585061 +30.489168 12.984 0.045 203.604285 +30.489077 12.955 0.052 SE 203.583747 +30.487513 12.942 0.048 203.602990 +30.487452 12.920 0.051 S 203.581823 +30.486427 12.949 0.058 203.601072 +30.486338 12.920 0.047 SW 203.579918 +30.487530 12.924 0.061 203.599144 +30.487453 12.963 0.048 W 203.578640 +30.489210 12.890 0.062 203.597877 +30.489100 12.983 0.064 NW 203.579932 +30.490852 12.879 0.052 203.599169 +30.490753 12.930 0.064
From Rae Stiening:
8/16/2000 Subject: Latest Admirals' club summary 8th magnitude parent in center No star in center 5 pix circle 17 pix 8 pix 5 pix 15 px W 15 pix E N 12.986 12.917 12.764 12.962 13.055 ne 12.976 12.991 12.753 13.018 12.957 E 12.984 12.981 12.855 13.018 12.989 se 12.991 13.035 12.827 12.976 12.954 S 12.980 12.923 12.794 12.983 12.954 sw 12.994 12.947 12.886 12.958 12.997 W 12.958 12.997 12.995 12.924 13.017 nw 12.978 12.953 12.851 12.913 12.964 Average 12.981 12.968 12.841 12.969 12.986 The above magnitudes have been corrected for the 0.034 offset so 13 is the expected answer. The fact that the no star in center 5 pixel radius circle gives the same answer as the 17 pixel radius circle with an 8th magnitude star in the center shows that the 13th magnitude stars do not contaminate each other in the 5 pixel radius configuration. Hence it appears that the 0.15 magnitude bias at the 5 pixel radius with the bright star in the center is a result of contamination of the photometry by the haze around the bright star.
Eric Howard has generated plots showing the brightness of the simulated stars as a function of separation from the parent star. Eric's description:
This set of graphs plot mags as a funciton of distance from the central star with appropriate error bars (1 sigma) for 9th, 13th, 14th, and 15th magnitude secondary stars. Plots are now correctly labeled with pixels (not arc sec) and are plotted on the same scale (+/- 1 mag). eric
